Spear head assemblies are well known in the art of ground drilling and are typically used to provide a releasable connection between, a running tool or other apparatus which is required to be lowered into and/or retrieved from a ground drill or bore hole, and; a wire line located at the ground surface. An overshot is attached to one end of the wire line which is able to selectively grab and then release a spear head assembly.
The spear head assembly is often formed integrally with the running tool or apparatus although sometimes it is formed as a separate unit and then attached to the tool or apparatus. Known spear head assemblies typically include a fixed spear point which extends in the axial direction and points upwardly for engagement with the overshot.
A difficulty encountered with the use of known spear head assemblies is that they tend to act as a plug and substantially reduce the flow of mud or other drilling fluids along or through the running tool or apparatus to which they are attached, or the drill pipe or bore in which they are disposed.
A further difficulty with known spear head assemblies is that when the running tool or apparatus to which they are attached is removed from the ground, very high loads are placed on a shank portion of the spear point and a jar bar of the overshot. These loads can cause bending or breakage of the shank and jar bar. This increases the cost of drilling due to increased down time and equipment costs. Moreover, in the case of breakage, personal injury and death can result as very heavy pieces of drilling equipment can fall uncontrollably.